Influence of Atomization on the Particle Formation in Spray Flames

RICARDO TISCHENDORF, Fabian Fröde, Temistocle Grenga, Heinz Pitsch, Manuel Reddemann, Reinhold Kneer, Hans-Joachim Schmid, Sophie Dupont, University of Paderborn, Germany

     Abstract Number: 201
     Working Group: Nanoparticles and Materials Synthesis

Abstract
The synthesis of nanoparticles by Spray Flame Pyrolysis (FSP) enables the production of industrially relevant materials with tailored properties and offers several advantages in comparison to established gas phase synthesis. However, the FSP synthesis chain involves a large number of simultaneous occurring physical and chemical sub-processes, which contributes to a high degree of process complexity and makes it hard to control. As initial step a liquid precursor mixture is atomized via a nozzle into a self-sustaining gaseous pilot flame. Subsequently, the ignition of the precursor mixture components follows, and specific particle structure properties evolve as function of nucleation, coagulation and sintering processes.

Our investigations showed that the evolution of particle properties can be highly influenced by solely varying the nozzle geometry. In particular, particle size distribution widths, primary particle sizes, crystal phase polymorphisms and the elemental composition (product purity) can be influenced under otherwise identical process conditions (identical dimensionless numbers We, Re). In our study two different nozzle configurations and two precursor compositions leading to a synthesis of iron oxide nanoparticles were exemplary compared. The flame and droplet characteristics were characterized by shadowgraphy, PDA/LDA measurements and by high-speed imaging. Particle samples were extracted in situ along the flame by using two complementary techniques, namely a hole in a tube diluter and a thermophoretic sampler system. The final particle outcome was comprehensively analyzed by state-of-the-art powder characterization techniques (FTIR and Raman spectroscopy, HRTEM, XRD, TGA-DSC-MS, BET, magnetometry). It was revealed that the precursor ignition as well as the particle residence times in high temperature regions are highly affected by the atomization principle.